Following the hertz contact and raceway control theory of the ball screw and considering the centrifugal force and gyroscopic moment acting on the ball screw, the dynamic model of high-speed ball screw was set up with consideration of pretension. The effects of different working conditions, such as the running speed and the axial preload, on the mechanical properties of the ball screw were studied and solved through numerical analysis. The result has shown that these factors affect the dynamic characteristic of ball screw dramatically, and the dynamic characteristic of ball screw at high speed is greatly different from that of ball screw at low speed.